The area of the invention is drilling rigs for deep oil and gas boreholes, and for the equipment within the drilling rig for handling and maneuvering the drill string.
The standard form of drilling rig utilized today consists of two major structural components which are addressed by the invention. The first is a substructure with sufficient height to accommodate a stack of blow out preventers (BOP) underneath the substructure, and with sufficient strength to support the entire drilling rig and drill string. A rotary table mounted at the substructure floor drives the string while drilling and supports the drill string, by means of removable slips and elevators, during makeup and break out of the string. When the string is removed from the borehole, it is racked (stored) on the substructure in a setback area, at rig floor level.
The second component is the mast, which is mounted onto and above the substructure. This mast must have sufficient height to accommodate a drill pipe stand, together with all hoisting tools (block, lines, hook, links, and elevators) required to hoist the pipe string. Drill string is usually handled as three joined sections, or joints, of standard drill pipe which are coupled together; each joint of standard drill pipe is approximately 31 (thirty-one) feet long, and this triple section is therefore about 93 feet long. Thus the working height of the mast must be the combination of the stand (93 feet), the tools (usually 30 feet), an attachment working area above the substructure floor (about 4 feet), and a safety factor between the top of the hoisting block and the mast crown (about 10 feet). This is a minimum of 137 feet; in fact the typical large rig has a 142 foot mast mounted on a 25 to 30 foot high substructure.
It is apparent then that all the height and bulk of the mast and substructure combination, beyond that required to add drill pipe to the string (make connections) and to support the drill string suspended down hole, is to accommodate the handling of string in units of more than one joint. This is a trade off between rig complexity and size versus the time saved when making trips from not having to make up every joint connection each time the drill string is placed or removed. If it were not for this need to save time by setting back pipe in lengths greater than single joints, no rig would have cause to be higher than a height to accommodate the hoisting tools, the kelly and one joint of pipe.
Several structures have addressed the need to increase the efficiency of this conventional pipe handling.
U.S. Pat. No. 3,266,582 TO HOMANICK discloses a drilling rig using horizontal racking of the drill pipe and a specifically designed drill head suspension assembly. A traveling block assembly which has two spaced apart sheaves axially aligned, one on each side of the center line of the drill rig is disclosed. The traveling block is a centrally suspended single traveling block handling the drill string from the top end.
U.S. Pat. No. 4,738,321 TO OLIVIER discloses a mechanism for handling a drill pipe by a gripper which clutches the pipe at a mid-point and which moves the gripped stand of pipe to a fingerboard for vertical rack storage. FIG. 2 appears to show the mechanism handling a double stand of pipe. Again, the pipe is positioned by a traveling block connected to the top end of the drill string.
U.S. Pat. No. 3,633,771 TO WOOLSLAYER ET AL. discloses a mechanism for handling a pipe triple for racking for horizontal storage. The mechanism is a double grip on a manipulable vertical beam which can be folded to place the pipe along a horizontal storage rack. The pipe string however is handled by a top end traveling block; the mechanism serves only to grip the pipe and does not otherwise support or manipulate the drill string.
U.S. Pat. No. 3,613,906 TO DEYO ET AL. discloses a drill pipe storage and racking mechanism for moving the pipe horizontally while in a vertical position out of the center line of the drill rig. The mechanism is notable in that it holds both the upper and lower end of the drill pipe; otherwise, there is no manipulation of the drill string or the pipe.
U.S. Pat. No. 4,440,536 TO SCAGGS discloses a mechanism for aligning drill pipe during the threading and unthreading operations; the device basically replaces the stabber and holds and aligns the pipe horizontally during the threading and unthreading. The pipe, however, remains suspended from a central traveling block and apparently tongs and the like are required to actually rotate the pipe.
U.S. Pat. No. 5,244,329 TO MCGILL ET AL. shows a mechanism for handling a pipe triple within a fingerboard of a vertical pipe rack, comprising a set of upper and lower mounted jaws connected to operating arms which grip and position the pipe.
U.S. Pat. No. 5,265,683 TO KRASNOV shows a moving rotary drive system for replacing the Kelly or Kelly Bushing. The rotary bushing is mounted on a mobile platform which is raised or lowered a distance above the rotary table by means of hydraulic cylinders. The invention discloses a gripper system for gripping and rotating a pipe within the moveable platform. The platform is described as being moveable upward or downward a selected distance for drilling and reaming operations. The pipe string itself is still raised and lowered by means of a traveling block and crown assembly.
U.S. Pat. No. 3,365,008 TO ZIMMERMAN ET AL. discloses, as part of a drilling rig for drilling ultra large diameter holes, the structural concept of constructing the drilling rig in the form of two parallel spaced apart vertical load-supporting members with the pipe handling equipment being suspended between the load supporting members.